BCM Code B124 - Vehicle Speed Sensor Circuit: Notes

The vehicle speed sensor (VSS) uses a permanent magnet generator to produce an electrical signal representative of vehicle speed. This signal is sent to the BCM by circuit No. 400 (VSS HI) and circuit No. 401 (VSS LO) where the BCM buffers and amplifies the signal for its different uses. Output of the generator can be seen by using a digital voltmeter (A/C scale) while rotating the generator drive (rotating front wheels).

Code B124 will set when ignition is on, no code B334 or EO28, no input to BCM from VSS, transaxle in 4th gear (°F status light), and engine speed greater than 1300 RPM. During a failure, the compressor at idle will be disabled and vehicle speed reading BD60 will display actual sensor reading.

1. Since the BCM amplifies and buffers the speed signal before its sent to the ECM, code E024 in ECM will be set along with code B124 in the BCM if permanent magnet generator or circuit Nos. 400 and 401 have a problem. If there is a problem with the vehicle speed sensor circuit, and no code EO24 is set, there is an internal problem with the BCM.
2. BCM data code BD60 displays MPH.
3. With front wheels turning, a voltage reading indicates that permanent magnet generator and wiring are okay.
4. Checks for an open in VSS circuit wiring.
5. Checks ground in VSS circuit wiring prior to replacing sensor.